This invention relates to mobile phone telephony, and particularly, but not exclusively, to mobile phone telephony involving the sending and receiving of text messages using the short message service (SMS).
Conventionally, mobile phone telephony networks include mobile switching centres (MSCs) for switching of application part messages, for example mobile application part (MAP) messages or CAMEL application part (CAP) messages, around the network from sender to receiver, and service control points (SCPs) which provide intelligent networks (INs) for control of the handling of the messages in the network according to a call model such as CAMEL2 (Customized Applications for Mobile Network Enhanced Logic 2). For example, speech messages sent from a pre-pay mobile phone are switched by an MSC to a receiver. The MSC alerts an SCP that a call has been made, and the SCP debits the account of the sender. In the case of SMS text messages, however, these are switched by an MSC to a short message service centre (SMSC) and on to the receiver. Neither the MSC nor the SMSC alerts the SCP that a message has been sent, and the SCP cannot therefore charge for the message at the time it is sent. Instead the SMS text message can only be charged for once it has reached the SMSC, this is usually achieved by down-loading message details for post-processing off-line. By the time this is achieved, the recipient may already have retrieved the message. The sender may be using a pre-pay mobile phone and may not have had sufficient credit to send the SMS text message. This is only detected after the message has been sent to the SMSC, i.e. delivery of the message can be effectively free which is undesirable to the network providers. It is desirable for credit to be checked and charges levied before onward transmission of the SMS text message to the SMSC. Onward transmission can thereby be prevented if the sender bas insufficient credit.